Core Web Vitals in Plain English
Core Web Vitals get discussed as if they were an arcane compliance exercise. They are three measurements of things that annoy real people, and each has a small set of usual causes.
Largest Contentful Paint: how fast did the main thing appear?
Measures when the biggest element in the viewport finishes rendering, usually a hero image or a headline. Aim for under 2.5 seconds on mobile. Usual causes of failure:
- An oversized hero image, or one that is lazy loaded when it should not be.
- Slow server response, often from uncached pages or a struggling host.
- Fonts and stylesheets that block rendering.
- A slider that has to initialize before anything shows.
Interaction to Next Paint: does it respond when I tap?
Measures the delay between an interaction and the page visibly reacting. Aim for under 200 milliseconds. Usual causes:
- Too much JavaScript running on the main thread, particularly from page builders and analytics stacks.
- Chat widgets, popups, and tracking scripts loading during the first seconds.
- Heavy work bound to scroll or input events.
Cumulative Layout Shift: does it hold still?
Measures how much content jumps while loading. Aim for under 0.1. Usual causes:
- Images and videos without width and height attributes.
- Ads or embeds inserted without reserved space.
- Web fonts swapping in and reflowing text.
- Banners injected at the top of the page after render, which is why people tap the wrong thing.
Where to get real numbers
Lab tools estimate; field data from real visitors is what counts, and it is available in Search Console and in the Chrome UX report. Judge yourself on the 75th percentile of mobile field data, not on a lab score from your laptop.
How much this matters for ranking
These are a tiebreaker, not a primary factor. Content and relevance decide most rankings. But the same fixes that satisfy the metrics also stop visitors from leaving, so the ranking question is somewhat beside the point.
